settings_ui: Move settings UI trait to file content (#37337)

Closes #ISSUE

Initially, the `SettingsUi` trait was tied to `Settings`, however, given
that the `Settings::FileContent` type (which may be the same as the type
that implements `Settings`) will be the type that more directly maps to
the JSON structure (and therefore have the documentation, correct field
names (or `serde` rename attributes), etc) it makes more sense to have
the deriving of `SettingsUi` occur on the `FileContent` type rather than
the `Settings` type.

In order for this to work a relatively important change had to be made
to the derive macro, that being that it now "unwraps" options into their
inner type, so a field with type `Option<Foo>` where `Foo: SettingsUi`
will treat the field as if it were just `Foo`, expecting there to be a
default set in `default.json`. This imposes some restrictions on what
`Settings::FileContent` can be as seen in 1e19398 where `FileContent`
itself can't be optional without manually implementing `SettingsUi`, as
well as introducing some risk that if the `FileContent` type has
`serde(default)`, the default value will override the default value from
`default.json` in the UI even though it may differ (but it should!).

A future PR should probably replace the other settings with `FileContent
= Option<T>` (all of which currently have `T == bool`) with wrapper
structs and have `KEY = None` so the further niceties
`derive(SettingsUi)` will provide such as path renaming, custom UI, auto
naming and doc comment extraction can be used.

Release Notes:

- N/A *or* Added/Fixed/Improved ...

crates/workspace/src/item.rs

@@ -49,7 +49,7 @@ impl Default for SaveOptions {
     }
 }
 
-#[derive(Deserialize, SettingsUi)]
+#[derive(Deserialize)]
 pub struct ItemSettings {
     pub git_status: bool,
     pub close_position: ClosePosition,
@@ -59,7 +59,7 @@ pub struct ItemSettings {
     pub show_close_button: ShowCloseButton,
 }
 
-#[derive(Deserialize, SettingsUi)]
+#[derive(Deserialize)]
 pub struct PreviewTabsSettings {
     pub enabled: bool,
     pub enable_preview_from_file_finder: bool,
@@ -101,7 +101,7 @@ pub enum ActivateOnClose {
     LeftNeighbour,
 }
 
-#[derive(Clone, Default, Serialize, Deserialize, JsonSchema)]
+#[derive(Clone, Default, Serialize, Deserialize, JsonSchema, SettingsUi)]
 pub struct ItemSettingsContent {
     /// Whether to show the Git file status on a tab item.
     ///
@@ -130,7 +130,7 @@ pub struct ItemSettingsContent {
     show_close_button: Option<ShowCloseButton>,
 }
 
-#[derive(Clone, Default, Serialize, Deserialize, JsonSchema)]
+#[derive(Clone, Default, Serialize, Deserialize, JsonSchema, SettingsUi)]
 pub struct PreviewTabsSettingsContent {
     /// Whether to show opened editors as preview tabs.
     /// Preview tabs do not stay open, are reused until explicitly set to be kept open opened (via double-click or editing) and show file names in italic.

crates/workspace/src/workspace_settings.rs

@@ -8,7 +8,7 @@ use schemars::JsonSchema;
 use serde::{Deserialize, Serialize};
 use settings::{Settings, SettingsSources, SettingsUi};
 
-#[derive(Deserialize, SettingsUi)]
+#[derive(Deserialize)]
 pub struct WorkspaceSettings {
     pub active_pane_modifiers: ActivePanelModifiers,
     pub bottom_dock_layout: BottomDockLayout,
@@ -118,7 +118,7 @@ pub enum RestoreOnStartupBehavior {
     LastSession,
 }
 
-#[derive(Clone, Default, Serialize, Deserialize, JsonSchema)]
+#[derive(Clone, Default, Serialize, Deserialize, JsonSchema, SettingsUi)]
 pub struct WorkspaceSettingsContent {
     /// Active pane styling settings.
     pub active_pane_modifiers: Option<ActivePanelModifiers>,
@@ -216,14 +216,14 @@ pub struct WorkspaceSettingsContent {
     pub zoomed_padding: Option<bool>,
 }
 
-#[derive(Deserialize, SettingsUi)]
+#[derive(Deserialize)]
 pub struct TabBarSettings {
     pub show: bool,
     pub show_nav_history_buttons: bool,
     pub show_tab_bar_buttons: bool,
 }
 
-#[derive(Clone, Default, Serialize, Deserialize, JsonSchema)]
+#[derive(Clone, Default, Serialize, Deserialize, JsonSchema, SettingsUi)]
 pub struct TabBarSettingsContent {
     /// Whether or not to show the tab bar in the editor.
     ///
@@ -266,7 +266,7 @@ pub enum PaneSplitDirectionVertical {
     Right,
 }
 
-#[derive(Copy, Clone, Debug, Serialize, Deserialize, JsonSchema)]
+#[derive(Copy, Clone, Debug, Serialize, Deserialize, JsonSchema, SettingsUi)]
 #[serde(rename_all = "snake_case")]
 pub struct CenteredLayoutSettings {
     /// The relative width of the left padding of the central pane from the